A diesel-electric locomotive typically includes a diesel engine coupled to drive a main alternator and one or more auxiliary alternators. The main alternator is coupled to power one or more traction motors, and the auxiliary alternators are coupled to power locomotive auxiliary electrical equipment, such as radiator fan motors, traction motor blowers, alternator blowers, air compressors, etc.
The auxiliary equipment has generally been operated at a different voltage than the operating voltage of the traction motors. For example, the traction motors may be typically operated at a relatively higher voltage, while the auxiliary equipment may be operated at a relatively lower voltage. The lower voltage operation may allow for the use of auxiliary equipment with relatively lower insulation ratings at their windings to handle correspondingly lower voltage spikes. Such spikes may repetitively (e.g., on every turn-on and turn-off) result from the switching operation of inverter drive circuitry, such as high-speed power switches (e.g., insulated gate bipolar transistor (IGBT) switches and the like) coupled to drive the equipment. Thus, if the voltage level of a common bus, or bus voltage, for powering both the traction motors and the auxiliary equipment were to be set to a sufficiently high voltage level appropriate for powering the traction motors, this would require auxiliary equipment with costlier insulation ratings to avoid potential insulation damage due to the correspondingly higher voltage spikes. It will be appreciated that the magnitude of the voltage spikes may be substantially amplified as a result of standing wave reflections that arise when the distances between the inverter (drive) and the load increases.
Accordingly, the designer may be faced with the choice of using separate power buses for the traction motors and the auxiliary equipment or may be faced with the choice of using costlier motors for the auxiliary equipment, if a common power bus is used. It will be appreciated that either of the foregoing choices incrementally adds to the cost and weight of the locomotive. Thus, there is a need of a practical and reliable power system that provides a cost-effective solution to overcome the above-described issues.